PVP in survival is a very regular occurrence so reviving quickly is a highly important factor most players in any play style will see this as the most important mitigating factor for purchasing premium in the first place. And as for the skill tree in survival mode this is even more important to have than in open-world mode due to water food bar, infection, bleeding damage, using medical items more efficiently etc. Not to mention with premium, deluxe, extreme accounts you receive increased xp for zombie kills.